I suppose at this point most people don't remember that in the 20th century the Multiple Listing Service was a private database that only registered agents could access. So your average buyer had to hire an agent just to get a good idea of what was on the market. The upside of this is that the MLS did a lot to make the housing market rational, with more accurate and consistent pricing. So a house became a better investment. A lot of people thought that was worth the commissions. YMMV.

In the early 2000's the NAR made a bet that they could make MLS listings accessible to the public via the internet and maintain their business model. For decades the bet paid off, and people got the convenience of being able to do their own real estate shopping. But time seems to have run out on the payoff.

The smart move for the NAR at this point would simply be to take the MLS private again. Then buyer's agents would have leverage to contract for a minimum commission regardless of what sellers were offering. If sellers decided to offer little to no buyer's agent commission, then a lot of deals would fall apart when buyers realized how much they'd have to cough up in cash to cover the buyer's commission at closing. The alternative would be either for sellers to offer competitive buyer's commissions, or for the buyer's and seller's agents to make a side deal to roll the buyer's commission into the mortgage financing agreement.

The net result would be the same as the current situation, less buyer's money going to the seller -- but instead of everyone seeing the commission numbers up front, the question of whether the buyers could actually afford the house would be pushed later into the deal process, more money would go to lawyers to sort things out, and more time wasted by all parties in busted deals.

If the DOJ forbids taking the MLS private, then the NAR would simply have no incentive to maintain it. Without it, I expect the market would revert to the previous wild-west status, where it would be much harder to value a house, and financing would be more difficult and time-consuming to arrange, with many deals falling apart amid such difficulties. If this scenario were to come to pass, I expect there would eventually be public clamor for a new deal that would be equivalent to the current arrangement, except for names and who referees.

The most interesting question in that scenario will be whether the new deal happens before or after a real estate market crash.

I have no idea what equivalent system if any there is be in Europe for fair and consistent pricing of houses, and listing of available units, and who pays for MLS equivalents, if they exist. I never hear that discussed in articles on this topic. I'd be interested to know more.